This invention relates to ink jet printheads. More particularly, the invention relates to an ink jet printhead having at least one printhead chip that includes a nozzle guard to protect the chip.
As set out in the material incorporated by reference, the Applicant has developed ink jet printheads that can span a print medium and incorporate up to 84 000 nozzle assemblies.
These printheads includes a number of printhead chips. The printhead chips include micro-electromechanical components which physically act on ink to eject ink from the printhead chips. Such components are delicate and require careful handling to avoid damage.
Applicant has conceived a means for protecting such chips.
According to the invention, there is provided an ink jet printhead which comprises
at least one printhead chip that comprises
a wafer substrate;
a plurality of nozzle arrangements positioned on the wafer substrate, each nozzle arrangement having nozzle chamber walls and a roof wall that define a nozzle chamber and a nozzle opening in fluid communication with said nozzle chamber; and
an actuator that is operatively arranged with respect to each nozzle arrangement to eject ink from said nozzle chamber through the nozzle opening on demand; and
a nozzle guard positioned over the printhead chip, the nozzle guard comprising a wafer substrate with a plurality of passages defined through the wafer substrate, each passage being in register with a respective nozzle opening and each passage having a diameter that is not greater than 4 times a diameter of an ink drop ejected from said respective nozzle opening.
Each passage may have a diameter that is not less than 1.05 times the diameter of said respective nozzle opening.
The wafer substrate of the nozzle guard may define a planar cover member that in turn defines the passages and a support structure that is interposed between the cover member and the printhead chip to support the cover member over the printhead chip. The support structure of the wafer substrate may define a number of openings that permit the ingress of air into a region between the printhead chip and the cover member, so that the air can pass through the passages.
In this specification, the term xe2x80x9cnozzlexe2x80x9d is to be understood as an element defining an opening and not the opening itself.
The nozzle may comprise a crown portion, defining the opening, and a skirt portion depending from the crown portion, the skirt portion forming a first part of a peripheral wall of the nozzle chamber.
The printhead may include an ink inlet aperture defined in a floor of the nozzle chamber, a bounding wall surrounding the aperture and defining a second part of the peripheral wall of the nozzle chamber. It will be appreciated that said skirt portion is displaceable relative to the substrate and, more particularly, towards and away from the substrate to effect ink ejection and nozzle chamber refill, respectively. Said bounding wall may then serve as an inhibiting means for inhibiting leakage of ink from the chamber. Preferably, the bounding wall has an inwardly directed lip portion or wiper portion which serves a sealing purpose, due to the viscosity of the ink and the spacing between said lip portion and the skirt portion, for inhibiting ink ejection when the nozzle is displaced towards the substrate.
Preferably, the actuator is a thermal bend actuator. Two beams may constitute the thermal bend actuator, one being an active beam and the other being a passive beam. By xe2x80x9cactive beamxe2x80x9d is meant that a current is caused to flow through the active beam upon activation of the actuator whereas there is no current flow through the passive beam. It will be appreciated that, due to the construction of the actuator, when a current flows through the active beam it is caused to expand due to resistive heating. Due to the fact that the passive beam is constrained, a bending motion is imparted to the connecting member for effecting displacement of the nozzle.
The beams may be anchored at one end to an anchor mounted on, and extending upwardly from, the substrate and connected at their opposed ends to the connecting member. The connecting member may comprise an arm having a first end connected to the actuator with the nozzle connected to an opposed end of the arm in a cantilevered manner. Thus, a bending moment at said first end of the arm is exaggerated at said opposed end to effect the required displacement of the nozzle.
The printhead may include a plurality of nozzles each with their associated actuators and connecting members, arranged on the substrate. Each nozzle, with its associated actuator and connecting member, may constitute a nozzle assembly.
The printhead may be formed by planar monolithic deposition, lithographic and etching processes and, more particularly, the nozzle assemblies may be formed on the printhead by these processes.
The substrate may include an integrated drive circuit layer. The integrated drive circuit layer may be formed using a CMOS fabrication process.